This invention relates to swing arm bracket assemblies for automated machinery. More particularly, this invention relates to swing arm bracket assemblies for automated letter sorting machines.
FIG. 1 shows a conventional swing arm bracket assembly 10 as installed in a letter sorting machine. The swing arm bracket assembly includes bracket 12, swing arm 14, and top plate 16. Shaft 18 extends through the swing arm bracket assembly and is coupled at one end to servo motor 20 by keyed coupling 22. Shaft 18, on its other end, and idler shaft support 24 on swing arm 14 have compound pulleys 28 attached thereto on which rubber belts 30 are driven. Idler shaft support 24 is positioned on swing arm 14 by belt adjustment bolt 26. In operation, independently rotatable swing arm 14 is tensioned against a letter stack to create friction between the rubber belts and the letters. This tension is provided by helical extension spring 32 which attaches to spring post 34 on the swing arm bracket assembly.
FIG. 2 shows a top view of the conventional swing arm bracket assembly. Top plate 16 is attached to bracket 12 by socket screws 36. Additionally, to insure true alignment of the top plate and bracket, hardened straight pins 38 are provided. Mounting holes 40 are provided in bracket 12 for attachment of the servo motor to the bottom thereof. Swing arm 14 has oblong holes 42 and through holes 44 for attachment and positioning, respectively, of idler shaft support 24 (shown in FIG. 1.)
FIG. 3 is a partial side sectional view of the swing arm bracket assembly of FIG. 2 taken along line 3--3. Shaft 18 includes lesser diameter portion 46 and greater diameter portion 48. Collar 50 is provided around the lesser diameter portion of the shaft where the shaft extends through top plate 16. Below collar 50 is bearing 52 which is press fit onto lesser diameter portion 46 of shaft 18 and is positioned in bearing bore 54 of top plate 16. This bearing is typically General Bearing Part No. 6201-2RS.
Swing arm 14 includes arm portion 58 and cylindrical sleeve portion 60. A first sleeve 56 is provided below bearing 52 to locate bearing 52 on the bearing journal of shaft 18. Within cylindrical sleeve portion 60 are two bearings 64 which are also press fit onto lesser diameter portion 46 of shaft 18 and whose axial movement is restrained by retaining rings 66. These bearings are typically General Bearing Part No. 6001-2RS. A second sleeve 68 is positioned below bearings 64 followed by bearing 70, which is identical to bearings 64, also press fit onto shaft 18.
The recommended shaft fillet radius for bearings 64 and 70 as specified by the manufacturer is a maximum of 0.012 inches. The fillet radius for shaft 18 in conventional swing arm bracket assembly 10 is typically 0.018.+-.0.002 inches.
Bearing 74 is press fit onto greater diameter portion 48 of shaft 18 and is typically General Bearing Part No. R10-2RS. Bracket 12 provides a bearing bore 72 for positioning bearing 74 therein and axial movement of the bearing is restrained by retaining rings 76.
In operation, it has been found that the above-described conventional swing arm bracket assembly suffers from significant disadvantages. In particular, the swing arm bracket assembly requires five bearing press fits over long lengths of shaft. Such operations increase the potential for shaft bending during assembly.
Additionally, the shaft is rotatably supported between the bearings located in bearing bore 54 in top plate 16 and bearing bore 72 in bracket 12. These bearing bores must therefore be line bored and the parts maintained in true alignment. Accordingly, hardened straight pins must be utilized.
Further, the conventional swing arm bracket assembly is overly complex to assemble. Three different size bearings are used and the numerous snap rings inhibit assembly and disassembly of the structure.
Still further, the shaft fillet radius exceeds the recommended bearing design fillet radius which decreases the bearing internal clearance resulting in premature bearing failure.
There is therefore a need in the art for a swing arm bracket assembly which is more durable and which more readily facilitates assembly and maintenance.